Human Herpesvirus 7 (HHV‑7) is an enveloped double‑stranded DNA virus of the Betaherpesvirinae subfamily. It is closely related to HHV‑6 and primarily infects CD4 T lymphocytes, establishing lifelong latency and occasionally integrating into host chromosomal telomeres.
Virology and Replication
HHV‑7 has an icosahedral capsid, a tegument rich in viral proteins and a lipid envelope containing glycoproteins that mediate attachment and entry. The virus uses the membrane glycoprotein gH/gL/gO complex and other viral glycoproteins to bind to CD4 and possibly other co‑receptors on T cells. Following entry, the 160 kb genome is transported to the nucleus, where replication proceeds via a cascade of immediate early, early and late gene expression. The replication cycle of HHV‑7 is slow compared with alphaherpesviruses, and infected cells may show cytopathic enlargement. The virus establishes latency by maintaining its genome as an episome or integrating into telomeric DNA, with very limited gene expression. Reactivation occurs under conditions of immunosuppression or T‑cell activation, leading to production of new virions. HHV‑7 is acquired mainly in childhood through salivary transmission, and seroprevalence approaches 70–90 percent in many populations.
Clinical Impact
Primary HHV‑7 infection is often asymptomatic or causes a nonspecific febrile illness. Some cases of roseola infantum (exanthem subitum) and febrile seizures have been attributed to HHV‑7, although HHV‑6B is the predominant cause. The virus can reactivate in immunocompromised individuals, particularly following hematopoietic stem cell or solid organ transplantation, and may contribute to fever, encephalitis, bone marrow suppression or graft dysfunction. HHV‑7 has also been detected in cases of drug‑induced hypersensitivity syndrome. Diagnosis is based on polymerase chain reaction for viral DNA in blood or cerebrospinal fluid, but interpretation is complicated by latent chromosomal integration. There is no specific antiviral therapy approved for HHV‑7; ganciclovir, foscarnet and cidofovir have in vitro activity and are sometimes used in severe disease. No vaccine exists, and prevention centers on monitoring high‑risk patients and managing immunosuppression. HHV‑7 is a common but often overlooked member of the human herpesvirus family. While usually benign, its capacity to persist and reactivate underlies its occasional role in childhood exanthems and complications in immunosuppressed patients. Related Terms: human herpesvirus 6B, exanthem subitum, febrile seizure, latency, transplant